There is an increasing need for better protection via barriers to liquids, bacteria, or viruses, without sacrificing comfort, e.g., breathability and absorbency, for disposable personal protective apparel and disposable absorbent articles.
Vapor or gas permeable, microporous “breathable” material that is permeable to vapors or gas yet substantially impermeable to liquid have been developed in the past. Breathability previously has been imparted in polymer films by using inorganic fillers in the film polymer formulation, extruding the filler/polymer formulation into a film, and then mechanically stretching the film sufficiently to create voids around the filler particles, to make the film breathable. In a subsequent separate process, the breathable film made with inorganic filler in such a manner can be laminated with a nonwoven web using adhesive or a point-bonding calendar to produce a soft, textile like composite. Monolithic membranes or films also have been previously developed that of polymer resins that allow the passage of water vapor because of the hydrophilic character of the resin itself. These previous monolithic membranes/films are “breathable” barriers in the sense that the film acts as a barrier to liquids, but have passages with cross-sectional sizes on a molecular scale formed by a polymerization process. The passages serve as conduits by which water (or other liquid) vapor molecules can pass through the film as a result of a concentration gradient across the monolithic membrane or film. This process is referred to as activated diffusion. However, raw materials for such monolithic “breathable” films are relatively expensive when compared to conventionally used polyolefins such as polyethylene and polypropylene and their copolymers. Solutions for imparting breathability in films that do not require specialty chemicals, and instead can use more economical and widely available raw materials are needed.
U.S. Pat. No. 6,087,551 relates to a multi-denier non-woven fabric suitable for use as a body side liner in disposable absorbent products having an absorbent core positioned between a non-woven fabric and a separately preformed, body fluid-impermeable backing sheet. The multi-denier non-woven fabric is made from an interconnected network thermoplastic polymer fibre elements comprising a homogeneous blend of high denier and low denier fibres.
U.S. Pat. No. 6,781,027, similar to U.S. Pat. No. 6,087,551, relates in part to a composite structure including a mixed denier nonwoven fabric made of a homogeneous blend of large and small denier fibres. U.S. Pat. No. 6,781,027, similar to similar to U.S. Pat. No. 6,087,551 as well as U.S. Pat. Nos. 6,595,042 and 6,946,585, shows a nonwoven fabric combined with a fluid impermeable backing sheet in a structure including an intervening absorbent core. The nonwoven fabric and backing sheet in these references appear to be combined as separately preformed layers.